Hydrogel polymeric compositions and methods

ABSTRACT

Some aspects of this disclosure relate to a method of treating an ophthalmic disease affecting an eye of a patient comprising forming a covalently-crosslinked hydrogel in situ at a peri-ocular, intra-ocular, or intra-vitreal site for controlled release of a therapeutic agent.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 12/485,192 filed Jun. 16, 2009 which is a continuation of U.S.patent application Ser. No. 11/825,848 filed Jul. 9, 2007, which arehereby incorporated by reference herein.

TECHNICAL FIELD

The technical field, in general, relates to synthetic polymeric resinsthat are hydrogel compositions, as applied to certain medicalconditions.

BACKGROUND

Age-related macular degeneration (AMD), diabetic retinopathy, diabeticmacular edema (DME) posterior uveitis, choroidal neovascularization(CNV) and cystoid macular edema (CME) are sight-threateningback-of-the-eye diseases. Age related macular degeneration and diabeticretinopathy are significant causes of visual impairment in the UnitedStates and elsewhere; these conditions are generally caused byangiogenesis (unwanted blood-vessel growth in the eye) that damages theretina and ultimately can cause blindness. Posterior uveitis is achronic inflammatory condition that causes about ten percent of theblindness in the United States.

SUMMARY

One invention disclosed herein is a crosslinked hydrogel formed in-situthat releases a therapeutic agent that can be used to treat back-of-theeye diseases. In this embodiment, aqueous polymeric precursors arecombined ex vivo in flowable concentrations/viscosities with a drug andinjected intravitreally or via subconjunctival routes through a smallgauge needle into the eye, where the precursors form a crosslinkedhydrogel that releases the drug over time. The hydrogel may beformulated to adhere to a tissue in or around the eye to enhance drugrelease effects and stability, to degrade to biocompatible componentswithout causing inflammation, and to crosslink in place. A shape-stablehydrogel thus formed can effectively deliver the drug and advantageouslyhave a well-controlled size, shape, and surface area. A small gaugeneedle or blunt tip cannula for sub-Tenon's injections may be used toinject the materials since soluble or flowable precursors may be usedinstead of an already-formed material.

A biocompatible material may be created for eye treatments, one thatcauses minimal inflammation. The hydrogels are made using biocompatibleprecursors, contain high proportions of water, and make biocompatibledegradation products. The materials may thus be soft, hydrophilic, andconforming to space where they are made, without hard edges, corners, orsharp surfaces.

Biodegradable materials can also be made that are effectivelyself-removing or, if removed, leave only portions that areself-removing. Some embodiments are implants made with a soft, flexiblebiomaterials crosslinked for strength so the implants they can be pulledout or otherwise evacuated though a small opening in case theirretrieval is needed.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 depicts anatomical features of an eye from a frontal view;

FIG. 2 is a partially cut-away perspective view of an eye;

FIG. 3 is a cross-sectional view of an eye; and

FIG. 4 is an enlarged view of the cross-sectional view of FIG. 3.

FIG. 5 depicts various delivery alternatives for the implants;

FIG. 6A depicts introduction of an implant into the eye, with a smallopening being made

FIG. 6B depicts the method of FIG. 6A, with a cannula introduced throughthe opening;

FIG. 6C depicts the method of FIG. 6B, with closure of the opening bycauterization

FIG. 7A depicts delivery of implants in the intravitreal space, with anopening being made on the eyes surface;

FIG. 7B depicts the method of FIG. 7A with a cannula for delivery of animplant to one or more locations internal to the eye;

FIG. 8 depicts delivery of a bolus of a material into an eye;

FIG. 9 depicts data gathered as per Example 2;

FIG. 10 depicts data gathered as per Example 3;

FIG. 11 depicts data gathered as per Example 4;

FIG. 12 depicts data gathered as per Example 5;

FIG. 13 depicts data gathered as per Example 6;

FIG. 14 depicts data gathered as per Example 7;

FIG. 15 depicts data gathered as per Example 8; and

FIG. 16 depicts data gathered as per Example 9.

DETAILED DESCRIPTION

Locally formed hydrogels made in-situ from precursors in aqueoussolution can serve as depots of drugs or other therapeutic agents forocular drug delivery. These depots can be formed as needed, e.g.,topically on the surface of the eye, trans-scleral in and/or between theconjunctival and scleral tissues, injected intraocularly, or formedperiocularly.

There are a variety of serious eye diseases that need treatment with adrug regimen. Described herein are hydrogels that can be formed in situon a tissue to deliver drugs. In situ refers to forming a material atits intended site of use. Thus a hydrogel may be formed in situ in apatient at the site wherein the hydrogel is intended to be used, e.g.,as a drug depot for controlled release.

The hydrogel is, in one embodiment, formed from precursors havingfunctional groups that form covalent crosslinks to crosslink thehydrogels and thereby form the hydrogel. The hydrogel delivers drugs tothe eye. Some embodiments use highly flowable precursors that gel slowlyenough to be forced through a very small bore cannula or needle toessentially cross-link only after injection, but nonetheless gel quicklyenough so that they do not migrate back through the track of theincision. This gel then swells minimally after crosslinking. The geldegrades in the physiological fluid in or around the eye without causinginflammation by degrading into parts that are biocompatible and notacidic. The hydrogel also has enough mechanical strength so that it canbe recovered by means of either manual or mechanicalirrigation/aspiration techniques if necessary. Moreover, in someembodiments the gel adheres to the tissue.

In general, precursors may be combined as described herein at a site inor near an eye to make a covalently-crosslinked hydrogel that comprisesa therapeutic agent that is released into the eye to treat an opthalmicdisease over a suitable period of time. The hydrogel may below-swelling, as measurable by the hydrogel having a weight increasingno more than about 10% or about 50% upon exposure to a physiologicalsolution for twenty-four hours relative to a weight of the hydrogel atthe time of formation; artisans will immediately appreciate that all theranges and values within the explicitly stated ranges are contemplated.The hydrogel also may be water-degradable, as measurable by the hydrogelbeing dissolvable in vitro in an excess of water by degradation ofwater-degradable groups in the hydrogel. A composition with theprecursors mixed therein can be introduced through a small-gauge needleprovided that the composition has a suitable viscosity, which in turndepends on precursor properties, concentrations, and chemistry. Further,the hydrogels' mechanical strengths and reaction time are adjustedthough control of the precursors and functional groups. The precursorsand hydrogels may have various features that can be mixed-and-matched asguided by the considerations for making an effective device; thefollowing sections describe some of these features.

Precursor Materials

The precursors can be triggered to react to form a crosslinked hydrogel.In general, the precursors are polymerizable and include crosslinkersthat are often, but not always, polymerizable precursors. Polymerizableprecursors are thus precursors that have functional groups that reactwith each other to form polymers made of repeating units.

Some precursors thus react by chain-growth polymerization, also referredto as addition polymerization, and involve the linking together ofmonomers incorporating double or triple chemical bonds. Theseunsaturated monomers have extra internal bonds which are able to breakand link up with other monomers to form the repeating chain. Monomersare polymerizable molecules with at least one group that reacts withother groups to form a polymer. A macromonomer is a polymer or oligomerthat has at least one reactive group, often at the end, which enables itto act as a monomer; each macromonomer molecule is attached to thepolymer by reaction the reactive group. Thus macromonomers with two ormore monomers or other functional groups tend to form covalentcrosslinks. Addition polymerization is involved in the manufacture of,e.g., polypropylene or polyvinyl chloride. One type of additionpolymerization is living polymerization.

Some precursors thus react by condensation polymerization that occurswhen monomers bond together through condensation reactions. Typicallythese reactions can be achieved through reacting molecules incorporatingalcohol, amine or carboxylic acid (or other carboxyl derivative)functional groups. When an amine reacts with a carboxylic acid an amideor peptide bond is formed, with the release of water. Some condensationreactions follow a nucleophilic acyl substitution, e.g., as in U.S. Pat.No. 6,958,212, which is hereby incorporated by reference to the extentit does not contradict what is explicitly disclosed herein.

Some precursors react by a chain growth-step system. Chain growthpolymers are defined as polymers formed by the reaction of monomers ormacromonomers with a reactive center. A reactive center is a particularlocation within a chemical compound that is the center of a reaction inwhich the chemical is involved. In chain-growth polymer chemistry, thisis also the point of propagation for a growing chain. The reactivecenter is commonly radical, anionic, or cationic in nature, but can alsotake other forms. Chain growth-step systems include free radicalpolymerization, which involves a process of initiation, propagation andtermination. Initiation is the creation of free radicals necessary forpropagation, as created from radical initiators, e.g., organic peroxidemolecules. Termination occurs when a radical reacts in a way thatprevents further propagation. The most common method of termination isby coupling where two radical species react with each other forming asingle molecule.

Some precursors react by a step growth mechanism, and are polymersformed by the stepwise reaction between functional groups of monomers.Most step growth polymers are also classified as condensation polymers,but not all step growth polymers release condensates.

Monomers may be polymers or small molecules. A polymer is an organicmolecule formed by combining many smaller molecules (monomers) in aregular pattern, and includes those formed from at least two monomersand also oligomers, which is a term herein referring to polymers havingless than about 20 monomeric repeat units. A small molecule generallyrefers to a molecule that is less than about 2000 Daltons.

The precursors must thus be small molecules, such as acrylic acid orvinyl caprolactam, larger molecules containing polymerizable groups,such as acrylate-capped polyethylene glycol (PEG-diacrylate), or otherpolymers containing ethylenically-unsaturated groups, such as those ofU.S. Pat. No. 4,938,763 to Dunn et al, U.S. Pat. Nos. 5,100,992 and4,826,945 to Cohn et al, or U.S. Pat. Nos. 4,741,872 and 5,160,745 toDeLuca et al., each of which are hereby incorporated by reference to theextent they do not contradict what is explicitly disclosed herein.

To form covalently crosslinked hydrogels, the precursors must becrosslinked together. In general, polymeric precursors will formpolymers that will be joined to other polymeric precursors at two ormore points, with each point being a linkage to the same or differentpolymers. Precursors with at least two monomers can serve ascrosslinkers since each monomer can participate in the formation of adifferent growing polymer chain. In the case of monomers with a reactivecenter, each monomer effectively has one functional group for reactingwith other precursors. In the case of functional groups without areactive center, among others, crosslinking requires three or more suchfunctional groups on a precursor. For instance, manyelectrophilic-nucleophilic reactions consume the electrophilic andnucleophilic functional groups so that a third functional group isneeded for the precursor to form a crosslink. Such precursors thus mayhave three or more functional groups and may be crosslinked byprecursors with two or more functional groups. Thus some precursors havefunctional groups for participating in polymer and/or crosslinkformation but are free of polymerizable reactive centers or are free ofradical and/or anionic and/or cationic reactive centers, or have onlysome combination of the same. A crosslinked molecule may be crosslinkedvia an ionic or covalent bond, a physical force, or other attraction. Acovalent crosslink, however, will typically offer stability andpredictability in reactant product architecture.

In some embodiments, each precursor is multifunctional, meaning that itcomprises two or more electrophilic or nucleophilic functional groups,such that a nucleophilic functional group on one precursor may reactwith an electrophilic functional group on another precursor to form acovalent bond. At least one of the precursors comprises more than twofunctional groups, so that, as a result of electrophilic-nucleophilicreactions, the precursors combine to form crosslinked polymericproducts.

The precursors may have biologically inert and water soluble portions,e.g., a core. A core refers to a contiguous portion of a molecule thatis generally at least about 80% of the molecule by weight, sometimeswith arms that extend from the core, with the arms having a functionalgroup, which is often at the terminus of the branch. A water solubleportion is a water soluble molecule or polymer that is joined to ahydrophobic polymer. The water soluble precursor or precursor portionpreferably has a solubility of at least 1 g/100 mL in an aqueoussolution. A water soluble portion may be, for instance, a polyether, forexample, polyalkylene oxides such as polyethylene glycol (PEG),polyethylene oxide (PEO), polyethylene oxide-co-polypropylene oxide(PPO), co-polyethylene oxide block or random copolymers, and polyvinylalcohol (PVA), poly (vinyl pyrrolidinone) (PVP), poly (amino acids,dextran, or a protein. The precursors may have a polyalkylene glycolportion and may be polyethylene glycol based, with at least about 80% or90% by weight of the polymer comprising polyethylene oxide repeats. Thepolyethers and more particularly poly (oxyalkylenes) or poly (ethyleneglycol) or polyethylene glycol are generally hydrophilic.

A precursor may also be a macromolecule, which is a molecule having amolecular weight in the range of a few thousand to many millions. Insome embodiments, however, at least one of the precursors is a smallmolecule of about 1000 Da or less. The macromolecule, when reacted incombination with a small molecule of about 1000 Da or less, ispreferably at least five to fifty times greater in molecular weight thanthe small molecule and is preferably less than about 60,000 Da; artisanswill immediately appreciate that all the ranges and values within theexplicitly stated ranges are contemplated. A more preferred range is amacromolecule that is about seven to about thirty times greater inmolecular weight than the crosslinker and a most preferred range isabout ten to twenty times difference in weight. Further, amacromolecular molecular weight of 5,000 to 50,000 is useful, as is amolecular weight of 7,000 to 40,000 or a molecular weight of 10,000 to20,000.

Certain macromeric precursors are the crosslinkable, biodegradable,water-soluble macromers described in U.S. Pat. No. 5,410,016 to Hubbellet al, which is hereby incorporated herein by reference to the extent itdoes not contradict what is explicitly disclosed. These monomers arecharacterized by having at least two polymerizable groups, separated byat least one degradable region.

Synthetic precursors may be used. Synthetic refers to a molecule notfound in nature or not normally found in a human. Some syntheticpolymers are free of amino acids or free of amino acid sequences thatoccur in nature. Some synthetic molecules are polypeptides that are notfound in nature or are not normally found in a human body, e.g., di-,tri-, or tetra-lysine. Some synthetic molecules have amino acid residuesbut only have one, two, or three that are contiguous, with the aminoacids or clusters thereof being separated by non-natural polymers orgroups.

Alternatively, natural proteins or polysaccharides may be adapted foruse with these methods, e.g., collagens, fibrin(ogen)s, albumins,alginates, hyaluronic acid, and heparins. These natural molecules mayfurther include chemical derivitization, e.g., synthetic polymerdecorations. The natural molecule may be crosslinked via its nativenucleophiles or after it is derivatized with functional groups, e.g., asin U.S. Pat. Nos. 5,304,595, 5,324,775, 6,371,975, and 7,129,210, eachof which is hereby incorporated by reference to the extent it does notcontradict what is explicitly disclosed herein. Natural refers to amolecule found in nature. Natural polymers, for example proteins orglycosaminoglycans, e.g., collagen, fibrinogen, albumin, and fibrin, maybe crosslinked using reactive precursor species with electrophilicfunctional groups. Natural polymers normally found in the body areproteolytically degraded by proteases present in the body. Such polymersmay be re-acted via functional groups such as amines, thiols, orcarboxyls on their amino acids or derivatized to have activatablefunctional groups. While natural polymers may be used in hydrogels,their time to gelation and ultimate mechanical properties must becontrolled by appropriate introduction of additional functional groupsand selection of suitable reaction conditions, e.g., pH. In contrast,fibrin glues, which rely on polymerization of fibrinogen to form fibrin,have a limited range of mechanical properties, a limited range ofdegradability, and are not generally suited to many of the ophthalmictherapeutic applications that are available when hydrogels as describedherein are formulated.

Precursors may be made with a hydrophobic portion. In some cases, theprecursor is nonetheless soluble in water because it also has ahydrophilic portion. In other cases, the precursor makes dispersion inthe water (a suspension) but is nonetheless reactable to from acrosslinked material. Some hydrophobic portions may include a pluralityof alkyls, polypropylenes, alkyl chains, or other groups. Someprecursors with hydrophobic portions are sold under the trade namesPLURONIC F68, JEFFAMINE, or TECTRONIC. A hydrophobic portion is one thatis sufficiently hydrophobic to cause the macromer or copolymer toaggregate to form micelles in an aqueous continuous phase or one that,when tested by itself, is sufficiently hydrophobic to precipitate from,or otherwise change phase while within, an aqueous solution of water atpH from about 7 to about 7.5 at temperatures from about 30 to about 50degrees Centigrade.

Precursors may have, e.g., 2-100 arms, with each arm having a terminus,bearing in mind that some precursors may be dendrimers or other highlybranched materials. Thus hydrogels can be made, e.g., from a multi-armedprecursor with a first set of functional groups and a lowmolecular-weight precursor having a second set of functional groups. Forexample, a six-armed or eight-armed precursor may have hydrophilic arms,e.g., polyethylene glycol, terminated with primary amines, with themolecular weight of the arms being about 1,000 to about 40,000; artisanswill immediately appreciate that all ranges and values within theexplicitly stated bounds are contemplated. Such precursors may be mixedwith relatively smaller precursors, for example, molecules with amolecular weight of between about 100 and about 5000, or no more thanabout 800, 1000, 2000, or 5000 having at least about three functionalgroups, or between about 3 to about 16 functional groups; ordinaryartisans will appreciate that all ranges and values between theseexplicitly articulated values are contemplated. Such small molecules maybe polymers or non-polymers and natural or synthetic.

Some embodiments include a precursor that consists essentially of anoligopeptide sequence of no more than five residues, e.g., amino acidscomprising at least one amine, thiol, carboxyl, or hydroxyl side chain.A residue is an amino acid, either as occurring in nature or derivatizedthereof. The backbone of such an oligopeptide may be natural orsynthetic. In some embodiments, peptides of two or more amino acids arecombined with a synthetic backbone to make a precursor; certainembodiments of such precursors have a molecular weight in the range ofabout 100 to about 10,000 or about 300 to about 500 Artisans willimmediately appreciate that all ranges and values between theseexplicitly articulated bounds are contemplated.

Precursors may be prepared to be free of amino acid sequences cleavableby enzymes present at the site of introduction, including free ofmetalloproteinases and/or collagenases. Further, precursors may be madeto be free of all amino acids, or free of amino acid sequences of morethan about 50, 30, 20, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acids.Precursors may be non-proteins, meaning that they are not a naturallyoccurring protein and cannot be made by cleaving a naturally occurringprotein and cannot be made by adding synthetic materials to a protein.Precursors may be non-collagen, non-fibrin (ogen), non-hyaluronic acid,and non-albumin, meaning that they are not one of these proteins and arenot chemical derivatives of one of these proteins. The use ofnon-protein precursors and limited use of amino acid sequences can behelpful for avoiding immune reactions, avoiding unwanted cellrecognition, and avoiding the hazards associated with using proteinsderived from natural sources.

Peptides may be used as precursors. In general, peptides with less thanabout 10 residues are preferred, although larger sequences (e.g.,proteins) may be used. Artisans will immediately appreciate that everyrange and value within these explicit bounds is included, e.g. 1-10,2-9. 3-10, 1, 2, 3, 4, 5, 6, or 7. Some amino acids have nucleophilicgroups (e.g., primary amines or thiols) or groups that can bederivatized as needed to incorporate nucleophilic groups orelectrophilic groups (e.g., carboxyls or hydroxyls). Polyamino acidpolymers generated synthetically are normally considered to be syntheticif they are not found in nature and are engineered not to be identicalto naturally occurring biomolecules.

Some hydrogels are made with a polyethylene glycol-containing precursor.Polyethylene glycol (PEG, also referred to as polyethylene oxide) refersto a polymer with a repeat group (CH2CH2O)n, with n being at least 3. Apolymeric precursor having a polyethylene glycol thus has at least threeof these repeat groups connected to each other in a linear series. Thepolyethylene glycol content of a polymer or arm is calculated by addingup all of the polyethylene glycol groups on the polymer or arm, even ifthey are interrupted by other groups. Thus, an arm having at least 1000MW polyethylene glycol has enough CH2CH2O groups to total at least 1000MW. As is customary terminology in these arts, a polyethylene glycolpolymer does not necessarily terminate in a hydroxyl group.

Initiating Systems

Some precursors react using initiators. An initiator group is a chemicalgroup capable of initiating a free radical polymerization reaction. Forinstance, it may be present as a separate component, or as a pendentgroup on a precursor. Initiator groups include thermal initiators,photoactivatable initiators, and oxidation-reduction (redox) systems.Long wave UV and visible light photoactivatable initiators include, forexample, ethyl eosin groups, 2, 2-dimethoxy-2-phenyl acetophenonegroups, other acetophenone derivatives, thioxanthone groups,benzophenone groups, and camphorquinone groups. Examples of thermallyreactive initiators include 4, 4′ azobis (4-cyanopentanoic acid) groups,and analogs of benzoyl peroxide groups. Several commercially availablelow temperature free radical initiators, such as V-044, available fromWako Chemicals USA, Inc., Richmond, Va., may be used to initiate freeradical crosslinking reactions at body temperatures to form hydrogelcoatings with the aforementioned monomers.

Metal ions may be used either as an oxidizer or a reductant in redoxinitiating systems. For example, ferrous ions may be used in combinationwith a peroxide or hydroperoxide to initiate polymerization, or as partsof a polymerization system. In this case, the ferrous ions would serveas a reductant. Alternatively, metal ions may serve as an oxidant. Forexample, the ceric ion (4+ valence state of cerium) interacts withvarious organic groups, including carboxylic acids and urethanes, toremove an electron to the metal ion, and leave an initiating radicalbehind on the organic group. In such a system, the metal ion acts as anoxidizer. Potentially suitable metal ions for either role are any of thetransition metal ions, lanthanides and actinides, which have at leasttwo readily accessible oxidation states. Particularly useful metal ionshave at least two states separated by only one difference in charge. Ofthese, the most commonly used are ferric/ferrous; cupric/cuprous;ceric/cerous; cobaltic/cobaltous; vanadate V vs. IV; permanganate; andmanganic/manganous. Peroxygen containing compounds, such as peroxidesand hydroperoxides, including hydrogen peroxide, t-butyl hydroperoxide,t-butyl peroxide, benzoyl peroxide, cumyl peroxide may be used.

An example of an initiating system is the combination of a peroxygencompound in one solution, and a reactive ion, such as a transitionmetal, in another. In this case, no external initiators ofpolymerization are needed and polymerization proceeds spontaneously andwithout application of external energy or use of an external energysource when two complementary reactive functional groups containingmoieties interact at the application site.

Functional Groups

The precursors have functional groups that react with each other to formthe material in situ. The functional groups generally have reactivecenters for polymerization or react with each other inelectrophile-nucleophile reactions or are configured to participate inother polymerization reactions. Various aspects of polymerizationreactions are discussed in the precursors section herein.

Thus in some embodiments, precursors have a polymerizable group that isactivated by photoinitiation or redox systems as used in thepolymerization arts, e.g., or electrophilic functional groups that arecarbodiimidazole, sulfonyl chloride, chlorocarbonates,n-hydroxysuccinimidyl ester, succinimidyl ester or sulfasuccinimidylesters, or as in U.S. Pat. Nos. 5,410,016, or 6,149,931, each of whichare hereby incorporated by reference to the extent they do notcontradict what is explicitly disclosed herein. The nucleophilicfunctional groups may be, for example, amine, hydroxyl, carboxyl, andthiol. Another class of electrophiles are acyls, e.g., as in U.S. Pat.No. 6,958,212, which describes, among other things, Michaels additionschemes for reacting polymers.

Certain functional groups, such as alcohols or carboxylic acids, do notnormally react with other functional groups, such as amines, underphysiological conditions (e.g., pH 7.2-11.0, 37° C.). However, suchfunctional groups can be made more reactive by using an activating groupsuch as N-hydroxysuccinimide. Certain activating groups includecarbonyldiimidazole, sulfonyl chloride, aryl halides, sulfosuccinimidylesters, N-hydroxysuccinimidyl ester, succinimidyl ester, epoxide,aldehyde, maleimides, imidoesters and the like. The N-hydroxysuccinimideesters or N-hydroxysulfosuccinimide (NHS) groups are useful groups forcrosslinking of proteins or amine-containing polymers, e.g., aminoterminated polyethylene glycol. An advantage of an NHS-amine reaction isthat the reaction kinetics are favorable, but the gelation rate may beadjusted through pH or concentration. The NHS-amine crosslinkingreaction leads to formation of N-hydroxysuccinimide as a side product.Sulfonated or ethoxylated forms of N-hydroxysuccinimide have arelatively increased solubility in water and hence their rapid clearancefrom the body. The sulfonic acid salt on the succinimide ring does notalter the reactivity of NHS group with the primary amines. An NHS-aminecrosslinking reaction may be carried out in aqueous solutions and in thepresence of buffers, e.g., phosphate buffer (pH 5.0-7.5),triethanolamine buffer (pH 7.5-9.0), or borate buffer (pH 9.0-12), orsodium bicarbonate buffer (pH 9.0-10.0). Aqueous solutions of NHS basedcrosslinkers and functional polymers preferably are made just before thecros slinking reaction due to reaction of NHS groups with water. Thereaction rate of these groups may be delayed by keeping these solutionsat lower pH (pH 4-7).

In some embodiments, each precursor comprises only nucleophilic or onlyelectrophilic functional groups, so long as both nucleophilic andelectrophilic precursors are used in the crosslinking reaction. Thus,for example, if a crosslinker has nucleophilic functional groups such asamines, the functional polymer may have electrophilic functional groupssuch as N-hydroxysuccinimides. On the other hand, if a crosslinker haselectrophilic functional groups such as sulfosuccinimides, then thefunctional polymer may have nucleophilic functional groups such asamines or thiols. Thus, functional polymers such as proteins, poly(allylamine), or amine-terminated di-or multifunctional poly(ethylene glycol)can be used.

An arm on a hydrogel precursor refers to a linear chain of chemicalgroups that connect a crosslinkable functional group to polymer a core.Some embodiments are precursors with between 3 and 300 arms; artisanswill immediately appreciate that all the ranges and values within theexplicitly stated ranges are contemplated, e.g., 4 to 16, 8 to 100, orat least 6 arms. Precursors may be dendrimers, e.g., as in PatentApplication Pub. No's. US20040086479, US20040131582, WO07005249,WO07001926, WO06031358, or the U.S. counterparts thereof; dendrimers mayalso be useful as multifunctional precursors, e.g., as in U.S. PatentPub. No's. US20040131582, US20040086479 and PCT Applications No'sWO06031388 and WO06031388; all of which US and PCT applications arehereby incorporated by reference to the extent they do not contradictwhat is explicitly disclosed herein. Dendrimers are highly orderedpossess high surface area to volume ratios, and exhibit numerous endgroups for potential functionalization. Some dendrimers are regularlyordered, meaning that each arm has an identical structure. Somedendrimers have arms with a plurality of serial branches meaning that apolymer branches into at least two arms that each branch into at leasttwo more arms. Consequently, dendrimers tend to display lowpolydispersity indexes, low viscosities, and high solubility andmiscibility. Some embodiments are directed to dendrimers with arelatively high molecular weight used with a relatively lower molecularweight multifunctional precursor, with suitable functional groups on theprecursors. Other embodiments are directed to using dendrimersfunctionalized with electrophiles and/or nucleophiles. In someembodiments, the dendrimers serve as precursors with a relatively lowermolecular weight (e.g., less than about half, less than about one-third)than another crosslinking precursor, e.g., with a dendrimer beingbetween about 600 and about 3000 Da and a multifunctional precursorbeing between about 2000 to about 5000 Da. In some embodiments, theprecursor is a hydrophilic dendrimer, e.g., comprising PEG. In someembodiments, each dendrimer arm, or at least half of the arms,terminates in a functional group for reaction with functional groups onother precursors. In some embodiments, dendrimer precursors of at leastabout 10,000 molecular weight are reacted with small precursors thatcrosslink the dendrimers, with the small precursors having a molecularweight of less than about 1000. In some embodiments, at least about 90%by number of the arms of the dendrimers are reacted to form links to thehydrogel; in other embodiments, less than about 25% by number of thearms are reacted so as to increase the mobility of the free arms.

One embodiment has reactive precursor species with 3 to 16 nucleophilicfunctional groups each and reactive precursor species with 2 to 12electrophilic functional groups each; artisans will immediatelyappreciate that all the ranges and values within the explicitly statedranges are contemplated.

Hydrogel Formation

In general, precursors may be combined in a flowable composition with adelayed crosslinking chemistry to make a covalently-crosslinked materialin situ that comprises a therapeutic agent that is released over asuitable period of time. The crosslinking reactions generally occur inaqueous solution under physiological conditions. The crosslinkingreactions preferably do not release heat of polymerization or requireexogenous energy sources for initiation or to trigger polymerization.Photochemical initiation, for instance, is generally to be avoided inthe eye so as to avoid damage to the eye. In the case of injectedmaterials, the viscosity may be controlled so that the material isintroduced through a small diameter catheter or needle. In the case ofmaterials applied around an eye, which are optionally delivered throughsuch a catheter/needle, viscosity may further be controlled to keepprecursors in place until they form a gel so that the precursors do notrun-off the intended site of use.

The hydrogel is generally low-swelling, as measurable by the hydrogelhaving a weight increasing no more than about 0% to about 10% or toabout 50% upon exposure to a physiological solution for twenty-fourhours relative to a weight of the hydrogel at the time of formation. Oneembodiment for reducing swelling is to increase the number ofcrosslinks, bearing in mind, however, that cros slinks can increaserigidity or brittleness. Another embodiment is to reduce the averagechain distance between crosslinks. Another embodiment is to useprecursors with many arms, as explained below.

Another embodiment to reduce swelling is to control the degree ofhydrophilicity, with less hydrophilic materials tending to swell less;for instance, highly hydrophilic materials such as PEOs can be combinedwith less hydrophilic materials such as PPO or even hydrophobic groupssuch as alkyls.

Another embodiment to reduce swelling is to choose precursors that havea high degree of solvation at the time of crosslinking but subsequentlybecome less solvated and having a radius of solvation that effectivelyshrinks; in other words, the precursor is spread-out in solution whencrosslinked but later contracts. Changes to pH, temperature, solidsconcentration, and solvent environment can cause such changes; moreover,an increase in the number of branches (with other factors being heldeffectively constant) will tend to also have this effect. The number ofarms are believed to stericly hinder each other so that they spread-outbefore crosslinking, but these steric effects are offset by otherfactors after polymerization. In some embodiments, precursors have aplurality of similar charges so as to achieve these effects, e.g., aplurality of functional groups having a negative charge, or a pluralityof arms each having a positive charge, or each arm having a functionalgroup of similar charges before crosslinking or other reaction.

Hydrogels described herein can include hydrogels that swell minimallyafter deposition. Such medical low-swellable hydrogels may have a weightupon polymerization that increases no more than, e.g., about 50%, about10%, about 5%, about 0% by weight upon exposure to a physiologicalsolution, or that shrink (decrease in weight and volume), e.g., by atleast about 5%, at least about 10%, or more. Artisans will immediatelyappreciate that all ranges and values within or otherwise relating tothese explicitly articulated limits are disclosed herein. Unlessotherwise indicated, swelling of a hydrogel relates to its change involume (or weight) between the time of its formation when crosslinkingis effectively complete and the time after being placed in vitro aphysiological solution in an unconstrained state for twenty-four hours,at which point it may be reasonably assumed to have achieved itsequilibrium swelling state. For most embodiments, cros slinking iseffectively complete within no more than about fifteen minutes such thatthe initial weight can generally be noted at about 15 minutes afterformation as Weight at initial formation. Accordingly, this formula isused: % swelling=[(Weight at 24 hours−Weight at initialformation)/Weight at initial formation]*100. n the case of hydrogelsthat have substantial degradation over twenty-four hours, the maximumweight may be used instead of a 24-hour weight, e.g., as measured bytaking successive measurements. The weight of the hydrogel includes theweight of the solution in the hydrogel. A hydrogel formed in a locationwherein it is constrained is not necessarily a low-swelling hydrogel.For instance, a swellable hydrogel created in a body may be constrainedfrom swelling by its surroundings but nonetheless may be a highlyswellable hydrogel as evidenced by measurements of its swelling whenunconstrained and/or the forces against a constraint.

Reaction kinetics are generally controlled in light of the particularfunctional groups unless an external initiator or chain transfer agentis required, in which case triggering the initiator or manipulating thetransfer agent can be a controlling step. In some embodiments, themolecular weights of the precursors are used to affect reaction times.Precursors with lower molecular weights tend to speed the reaction, sothat some embodiments have at least one precursor with a molecularweight of at least 5,000 to 50,000 or 150,000 Daltons. Preferably thecrosslinking reaction leading to gelation occurs within about 2 to about10 or to about 30 minutes; artisans will immediately appreciate that allthe ranges and values within the explicitly stated ranges arecontemplated, e.g., at least 120 seconds, or between 180 to 600 seconds.Gelation time is measured by applying the precursors to a flat surfaceand determining the time at which there is substantially no flow downthe surface when it is titled at an angle of about 60 degrees (i.e., asteep angle, close to perpendicular).

The crosslinking density of the resultant biocompatible crosslinkedpolymer is controlled by the overall molecular weight of the crosslinkerand functional polymer and the number of functional groups available permolecule. A lower molecular weight between crosslinks such as 500 willgive much higher crosslinking density as compared to a higher molecularweight such as 10,000. The crosslinking density also may be controlledby the overall percent solids of the crosslinker and functional polymersolutions. Increasing the percent solids increases the probability thatan electrophilic functional group will combine with a nucleophilicfunctional group prior to inactivation by hydrolysis. Yet another methodto control crosslink density is by adjusting the stoichiometry ofnucleophilic functional groups to electrophilic functional groups. A oneto one ratio leads to the highest crosslink density. Precursors withlonger distances between crosslinks are generally softer, morecompliant, and more elastic. Thus an increased length of a water-solublesegment, such as a polyethylene glycol, tends to enhance elasticity toproduce desirable physical properties. Thus certain embodiments aredirected to precursors with water soluble segments having molecularweights in the range of 3,000 to 100,000 or, e.g., 10,000 to 35,000.

The solids content of the hydrogel can affect its mechanical propertiesand biocompatibility and reflects a balance between competingrequirements. In general, a relatively low solids content tends to bemost useful, e.g., between about 2.5% to about 25%, including all rangesand values there between, e.g., about 2.5% to about 10%, about 5% toabout 15%, or less than about 15%.

Anatomy of the Eye

The structure of the mammalian eye can be divided into three main layersor tunics: the fibrous tunic, the vascular tunic, and the nervous tunic.The fibrous tunic, also known as the tunica fibrosa oculi, is the outerlayer of the eyeball consisting of the cornea and sclera. The sclera isthe supporting wall of the eye and gives the eye most of its whitecolor. It is extends from the cornea (the clear front section of theeye) to the optic nerve at the back of the eye. The sclera is a fibrous,elastic and protective tissue, composed of tightly packed collagenfibrils, containing about 70% water.

Overlaying the fibrous tunic is the conjunctiva. The conjunctiva is amembrane that covers the sclera (white part of the eye) and lines theinside of the eyelids. It helps lubricate the eye by producing mucus andtears, although a smaller volume of tears than the lacrimal gland. Theconjunctiva is typically divided into three parts: (a) Palpebral ortarsal conjunctivam which is the conjunctiva lining the eyelids; thepalpebral conjunctiva is reflected at the superior fornix and theinferior fornix to become the bulbar conjunctiva. (b) Fornixconjunctiva: the conjunctiva where the inner part of the eyelids and theeyeball meet. (c) Bulbar or ocular conjunctiva: The conjunctiva coveringthe eyeball, over the sclera. This region of the conjunctiva is boundtightly and moves with the eyeball movements.

The conjunctiva effectively surrounds, covers, and adheres to thesclera. It is has cellular and connective tissue, is somewhat elastic,and can be removed, teased away, or otherwise taken down to expose asurface area of the sclera. As explained below, it can be removed orused in conjunction with transcleral drug delivery schemes.

The vascular tunic, also known as the tunica vasculosa oculi, is themiddle vascularized layer which includes the iris, ciliary body, andchoroid. The choroid contains blood vessels that supply the retinalcells with oxygen and remove the waste products of respiration.

The nervous tunic, also known as the tunica nervosa oculi, is the innersensory which includes the retina. The retina contains thephotosensitive rod and cone cells and associated neurons. The retina isa relatively smooth (but curved) layer. It does have two points at whichit is different; the fovea and optic disc. The fovea is a dip in theretina directly opposite the lens, which is densely packed with conecells. The fovea is part of the macula. The fovea is largely responsiblefor color vision in humans, and enables high acuity, which is necessaryin reading. The optic disc is a point on the retina where the opticnerve pierces the retina to connect to the nerve cells on its inside.

The mammalian eye can also be divided into two main segments: theanterior segment and the posterior segment. The anterior segmentconsists of an anterior and posterior chamber. The anterior chamber islocated in front of the iris and posterior to the corneal endotheliumand includes the pupil, iris, ciliary body and aqueous fluid. Theposterior chamber is located posterior to the iris and anterior to thevitreous face where the crystalline lens and zonules fibers arepositioned between an anterior and posterior capsule in an aqueousenvironment.

The cornea and lens help to converge light rays to focus onto theretina. The lens, behind the iris, is a convex, springy disk whichfocuses light, through the second humour, onto the retina. It isattached to the ciliary body via a ring of suspensory ligaments known asthe Zonule of Zinn. The ciliary muscle is relaxed to focus on an objectfar away, which stretches the fibers connecting it with the lens, thusflattening the lens. When the ciliary muscle contracts, the tension ofthe fibers decreases, which brings the lens back to a more convex andround shape. The iris, between the lens and the first humour, is apigmented ring of fibrovascular tissue and muscle fibers. Light mustfirst pass though the center of the iris, the pupil. The size of thepupil is actively adjusted by the circular and radial muscles tomaintain a relatively constant level of light entering the eye.

Light enters the eye, passes through the cornea, and into the first oftwo humors, the aqueous humour. Approximately two-thirds of the totaleyes refractive power comes from the cornea which has a fixed curvature.The aqueous humor is a clear mass which connects the cornea with thelens of the eye, helps maintain the convex shape of the cornea(necessary to the convergence of light at the lens) and provides thecorneal endothelium with nutrients.

The posterior segment is located posterior to the crystalline lens andin front of the retina. It represents approximately two-thirds of theeye that includes the anterior hyaloid membrane and all structuresbehind it: the vitreous humor, retina, c, and optic nerve. On the otherside of the lens is the second humour, the vitreous humour, which isbounded on all sides: by the lens, ciliary body, suspensory ligamentsand by the retina. It lets light through without refraction, helpsmaintain the shape of the eye and suspends the delicate lens.

FIG. 1 depicts eye 10 having sclera 12, iris 14, pupil 16, and eyelid18. FIG. 2 depicts a perspective view of eye 10 with a partialcross-section that depicts lens 20, inferior oblique muscle 22, inferiorrectus muscle 24, and optic nerve 26. FIG. 3 is a cross-section of eye10 and depicts cornea 22 that is optically clear and allows light topass iris 14 and penetrate lens 20. Anterior chamber 24 underlies cornea22 and posterior chamber 26 lies between iris 14 and lens 20. Ciliarybody 28 is connected to lens 20. FIG. 3 depicts a portion of theconjunctiva 30, which overlies the sclera 12. The vitreous body 32comprises the jelly-like vitreous humor, with hyaloid canal 34 being inthe same. Fovea 36 is in the macula and retina 38 overlies choroid 37.Zonular spaces 42 are depicted. FIG. 4 shows eye 10 in partial view, andshows portions of conjunctiva 30 on sclera 12, including tendon of thesuperior rectus muscle 44 emerging from the same.

FIG. 5 shows certain points of delivery at or near eye 10. One area istopically at 60, with area 60 being indicated by dots on surface of eye10. Another area is intravitreally as indicated by numeral 62, ortrans-sclerally, as indicated by numeral 64. In use, for example asyringe 66, catheter (not shown) or other device is used to deliverhydrogel or a hydrogel precursors, optionally through needle 68, intothe eye, either intravitrealy, as at 70 or peri-ocularly, as at 72.Drugs or other therapeutic agents are released to the intra-ocularspace. In the case of back-of-the-eye diseases, drugs may be targetedvia the peri-ocular or intravitreal route to target approximate area 74,where they interact with biological features to achieve a therapy.

Eye Disease States

The materials described herein may be used to deliver drugs or othertherapeutic agents (e.g., imaging agents or markers) to eyes or tissuesnearby. Some of the disease states are back-of-the-eye diseases. Theterm back-of-the eye disease is recognized by artisans in these fieldsof endeavor and generally refers to any ocular disease of the posteriorsegment that affects the vasculature and integrity of the retina, maculaor choroid leading to visual acuity disturbances, loss of sight orblindness. Disease states of the posterior segment may result from age,trauma, surgical interventions, and hereditary factors. Someback-of-the-eye disease are; age-related macular degeneration (AMD)cystoid macular edema (CME), diabetic macular edema (DME), posterioruveitis, and diabetic retinopathy. Some back-of-the-eye diseases resultfrom unwanted angiogenesis or vascular proliferation, such as maculardegeneration or diabetic retinopathy. Drug treatment options for theseand other conditions are further discussed elsewhere herein.

Application of Precursors to form Hydrogels In Situ

One mode of application is to apply a mixture of precursors and othermaterials (e.g., therapeutic agent, viscosifying agent, accelerator,initiator) through a needle, cannula, catheter, or hollow wire to a sitein or near an eye. The mixture may be delivered, for instance, using amanually controlled syringe or mechanically controlled syringe, e.g., asyringe pump. Alternatively, a dual syringe or multiple-barreled syringeor multi-lumen system may be used to mix the precursors at or near thesite.

One system that has been tested involved mixing a drug into a diluent,and drawing 200 microliters of the drug/diluent into a 1 ml syringe.About 66 mg of a precursor powder consisting of trilysine was placedinto a separate 1 ml syringe. The two syringes were attached via afemale-female LUER connector, the solution was moved back and forthbetween the syringes until the dry precursor was completely dissolved. Asolution of multi-armed electrophilic precursor in 200 μl of water wasdrawn into a third 1-ml syringe. Using another female-female LUERconnector, the user mixed the reconstituted PEG/drug solution with theelectrophilic precursor. The solutions were rapidly inject back andforth at least about ten times to ensure good mixing. The solutions weredrawn into 1 syringe and were then available for further use.

Sites where drug delivery depots may be formed include the anteriorchamber, the vitreous, episcleral, in the posterior subtenon's space(Inferior fornix), subconjunctival, on the surface of the cornea or theconjunctiva, among others.

Back of the eye diseases can be treated with drugs utilizing, e.g.,topical, systemic, intraocular and subconjunctival delivery routes.Systemic and topical drug delivery modalities fall short in deliveringtherapeutic drug levels to treat posterior segment diseases. Thesemethods of drug delivery encounter diffusion and drug dilution issuesdue to the inherent anatomical barriers of the intraocular and systemicsystems, causing significant patient side effects (due to multiple dailydosing), poor bioavailability and compliance issues. Pericular drugdelivery of an ophthalmic hydrogel implant using subconjunctival,retrobulbar or sub-Tenon's placement has the potential to offer a saferand enhanced drug delivery system to the retina compared to topical andsystemic routes.

The delivery site for placement of an intraocular drug delivery implantis generally dependent upon the disease that needs to be treated and thetype of drug therapy. For example; steroids like dexamethasone andtriamicinolone acetonide may be mixed with the hydrogel precursor toform a sustained-release drug implant. The liquid hydrogel could then beinjected in-situ into the sub-Tenon's capsule where it could deliver aconstant or tunable release profile of the drug over and over a three tofour month time period. The minimally invasive procedure could beperformed in a doctor's office, or after a cataract operation undertopical anesthesia, to treat chronic back of the eye diseases.

In some embodiments, a retractor 80 is used to hold back eyelids 82, andthe user would create a small buttonhole 84 (FIG. 6A) in the conjunctivaabout 5-6 mm from the inferior/nasal limbus and dissect the conjunctivadown through Tenon's capsule; to the bare sclera. Next, a 23-gauge bluntcannula 86 (e.g., 15 mm in length) is inserted through the opening andthe liquid drug implant is injected onto the scleral surface (FIG. 6B).The cannula is then removed and the conjunctive is closed with acauterization device 88 (FIG. 6C).

One advantage of an implant having three dimensional integrity is thatit will tend to resist cellular infiltration and be able to prevent thelocally administered drug from being phagocytosed and clearedprematurely from the site. Instead, it stays in place until delivered.By way of contrast a microparticle, liposome, or pegylated protein tendsto be rapidly cleared from the body by the reticuloendothelial systembefore being bioeffective.

Intravitreal Drug Delivery Implants

The delivery of therapeutic amounts of a drug to the retina in posteriorsegment eye diseases remains a challenge. Although intravitrealinjections into the vitreous cavity of anti-VEG F agents have shownpromise to arrest and in some cases reverse chronic age-related diseaseslike macular degeneration, these techniques and procedures are notwithout risks and side effects. Intravitreal administration oftherapeutic agents into the vitreous cavity can cause cataracts,endophthalmitis and retinal detachments. This form of therapy requiresmany patients to receive monthly intraocular injections of an anti-VEGFdrug over a 12 month time period thus increasing the risk of infection,vitreous wicks and retinal detachments. Embodiments directed to an insitu hydrogel biodegradable drug implant will provide an effectivealternative treatment for back of the eye diseases, and are expected toreduce the common side-effects associated with repeated intravitrealinjections. Embodiments of an intravitreal biodegradable drug deliveryimplant system are summarized below.

In FIG. 7A, a hydrogel implant is injected intravitrealy about 2.5 mmposterior to the limbus through a pars plana incision 90 using asub-retinal cannula 92, as shown by depiction of magnifying glass 94held so as to visualization incision 90 on eye 10, which may be madefollowing dissecting-away or otherwise clearing the conjunctiva, asneeded. A 25, 27 or 30 gauge sub-retinal cannula 94 (or otherappropriate cannulas) is then inserted through incision 90 andpositioned intraocularly to the desired target site, e.g., at least oneof sites 96, 98, 100 (FIG. 7B) where the flowable precursors areintroduced to form a hydrogel in-situ. The precursors then forms into anabsorbable gel 102, 104, and/or 106, adhering to the desired targetsite.

As described in more detail in other sections, a drug depot of thein-situ hydrogel drug delivery implant may be designed for controlled,long term drug release ranging from, e.g., about one to about threemonths; and may optionally be directed to treatment of diseases of theposterior segment including, for example, age-related maculardegeneration, diabetic retinopathy, diabetic macular edema, and thecystoid macular. The device can carry a drug payload of various types oftherapeutic agents for various conditions, of which some include, forexample, steroids, antibiotics, NSAIDS and/or antiangiogenic agents, orcombinations thereof.

The in-situ implant embodiments can improve the efficacy andpharmacokinetics of potent therapeutic agents in the treatment ofchronic back of the eye diseases and minimize patient side effects inseveral ways. First, the implant can be placed in the vitreous cavity ata specific disease site, bypassing the topical or systemic routes andthereby increasing drug bioavailability. Secondly, the implant maintainslocal therapeutic concentrations at the specific target tissue site overan extended period of time. Thirdly, the number of intravitrealinjections would be substantially reduced over a 12 month therapyregimen, thereby reducing patient risk of infection, retinal detachmentand transient visual acuity disturbances (white specks floating in thevitreous) that can occur until the drug in the vitreous migrates downtoward the inferior wall of the eye and away from the portion of thecentral vitreous or macula. As shown in FIG. 8, a bolus 120 ofconventionally-injected drugs forms in the vitreous body and displacesthe vitreous humor until dispersed. Dispersion typically takes asignificant amount of time since the vitreous humor is quite viscous.The bolus thus interferes with vision, particularly when it is movedaround the eye in response to sudden accelerations, e.g., as the patientstands up or quickly turns the head.

Trans-Scleral Drug Delivery

The hydrogels may be formed on scleral tissue either with or without thepresence of the conjunctiva. The hydrogel may be adhesive to the scleraor other tissue near the sclera to promote drug diffusion through theintended tissue or to provide a stable depot to direct the therapeuticagents as required. In some embodiments, the conjunctiva of the eye maybe removed, macerated, dissected away, or teased-free so that the tissuecan be lifted away from the sclera to access a specific region of thesclera for implantation or injection of the hydrogel. A hydrogel isformed in situ that makes a layer on, and adheres, to the surface area.The conjunctiva may be allowed to contact the tissue if it is stillpresent or retains adequate mechanical integrity to do so. In someembodiments the hydrogel is comprised of at least 50%, 75%, 80%, 90%, or99% w/w water-soluble precursors (calculated by measuring the weight ofthe hydrophilic precursors and dividing by the weight of all precursors,so that the weight of water or solvents or non-hydrogel components isignored) to enhance the non-adhesive properties of the hydrogel. In someembodiments, such hydrophilic precursors substantially comprise PEO s.In some embodiments, drugs to reduce tissue adherence mediated bybiological mechanisms including cell mitosis, cell migration, ormacrophage migration or activation, are included, e.g.,anti-inflammatories, anti-mitotics, antibiotics, PACLITAXEL, MITOMYCIN,or taxols.

In other embodiments, the sclera is not substantially cleared of theconjunctiva. The conjunctiva is a significant tissue mass that overlaysmuch or all of the sclera. The conjunctiva may be punctured orpenetrated with a needle or catheter or trocar and precursors introducedinto a space between the sclera and conjunctiva. In some cases theconjunctiva may be punctured to access a natural potential space betweenthe tissues that is filled by the precursors. In other cases, apotential or actual space is created mechanically with a trocar,spreader, or the like, that breaks the adherence between the sclera andconjunctiva so that precursors may be introduced. The conjunctiva hasenough elasticity to allow useful amounts of precursors to be introducedor forced into such natural or created spaces. Similarly, in the case ofintravitreal hydrogel formation, relatively large columns may also beused. Accordingly, in some cases, the amount is between about 0.25 toabout 10 ml; artisans will immediately appreciate that all the rangesand values within the explicitly stated ranges are contemplated, e.g.,about 1 ml or from 0.5 ml to about 1.5 ml.

Moreover, removal of a hydrogel, whether present intraocularly orperiocularly, is also readily achieved using either a vitrectomy cutterif the implant is located in the vitreous cavity or a manual I/A syringeand cannula if the implant is located on the scleral surface orirrigation/aspiration handpiece. This contrasts with major surgicalprocedures needed for the removal of some conventional non-absorbableimplants.

In some aspects, in-situ formation of the hydrogel lets the hydrogel gelor crosslink in place, so that it does not flow back out through thetract of the needle and diffuse extraocularly through the incision siteupon the removal of the needle or cannula. A shape-stable hydrogel thusformed can effectively deliver the drug and advantageously can havewell-controlled size, shape, and surface area. A small needle may beused to inject the materials since soluble or flowable precursors may beused instead of an already-formed material. By way of contrast,alternative materials that do not cross-link quickly and firmly uponintroduction tend to flow back out of the incision. And materials thatdo not covalently cross-link are subject to creep or weeping as thematerial continually reorganizes and some or all of the material flowsout.

Delivery across the sclera is an important advance in these arts that ismade possible by the hydrogels and other materials disclosed herein.Transcleral drug delivery would conventionally not be considered sincethe diffusion of the drug across the scleral tissue is an unknown. Notonly is the actual diffusion of the drug an issue, but the rate of thatpotential diffusion had to be balanced against the competing tendency ofthe drug to diffuse away to other relatively more permeable tissues,especially in response to tear or other fluid production. Moreover,fluid production in response to irritation is also a potential factor,e.g., as by flow of tears, lymph, edema, or a foreign body response. Butthe biocompatible materials and various available features, e.g.,softness, biocompatible degradation products, conformability tosurrounding tissues, adherence to the sclera, applicability over, in, orunder the conjunctiva, crosslinking, non-irritating shape and depositiontechniques, can be used to make suitable materials.

Adherence

Adhesivity can play an important role for in situ hydrogel-basedtherapies. For instance, a hydrogel that is adhesive to a scleral tissuecan have good surface-area contact with the sclera to promote diffusionof drugs or other agents into the sclera. By way of contrast, a failureto adhere will create a diffusion barrier or allow entry of fluidsbetween the drug depot and eye so that the drugs are washed away. On theother hand, if a peri-ocular hydrogel adheres to the tissues around it,or allows tissues to grow and adhere to it, the delivery of the drug maybe compromised. Thus a hydrogel depot that adheres tenaciously to thesclera (the hydrogel's anterior surface) but does not adhere to tissueson its opposing surface (the posterior surface for a coating) orsurfaces (for more complex geometries) would be useful. The in-situ madematerials can reconcile these opposing needs by allowing forming thematerial in situ on the sclera with its other surfaces being free orsubstantially free of tissue contact during the time of gelation and/orcrosslinking. As already explained, some embodiments relate to providinghydrogels that adhere to specific sites, e.g., the sclera and/orconjunctiva.

A test of adherence of a hydrogel to a tissue is, unless otherwiseindicated, to apply it to a rabbit cornea and show that it isimmobilized and is not displaced when placed on an uninjured rabbitcornea, despite unrestricted blinking by the rabbit. By way of contrast,a non-adherent material will be pushed out of, or to the side of theeye.

Some embodiments of forming a hydrogel involve mixing precursors thatsubstantially crosslink after application to a surface, e.g., on atissue of a patient to form a biodegradable hydrogel depot. Withoutlimiting the invention to a particular theory of operation, it isbelieved that reactive precursor species that crosslink after contactinga tissue surface will form a three dimensional structure that ismechanically interlocked with the coated tissue. This interlockingcontributes to adherence, intimate contact, and essentially continuouscoverage of the coated region of the tissue. Moreover, formulations withstrongly electrophilic functional groups may tend to react withnucleophilic groups on the tissue to form covalent crosslinks, providedthat the electrophiles are present in suitable concentrations and thenucleophiles are at a suitable pH.

By way of contrast, conventional materials tend to be non-adhesive to anocular surface. Lenticels made of hydrogels, for instance, are notadherent. Fibrin glue, for instance, is generally not adherent as thatterm is used herein, although the fact that it may stick somewhat to anocular tissue is acknowledged. Moreover, for many materials, it isgenerally unknown whether or not they will be adherent to an oculartissue, or to a particular ocular tissue.

Another aspect of adherence is that the implant is prevented from movingfrom the site of its intended use. This tends to increase patientcomfort, reduce irritation, and reduce tearing or fluid-flowingreactions that affect the therapeutic agent in the implant. Also, theimplant may be placed with precision, e.g., between certain tissues oron a tissue, with confidence that it will continue to affect theintended site.

Adherence can be useful for drug delivery. In some embodiments, specificzones are targeted for adherence, e.g., as in FIG. 5. For instance amaterial with the drug can be made to adhere to the sclera and/orconjunctiva. Or the material can be made to adhere to a surface insidethe eye, a surface in the anterior portion of the eye. In some cases,the material is targeted to adhere to a surface inside the eye andwithin 1-10 mm of the macula; artisans will immediately appreciate thatall the ranges and values within the explicitly stated ranges arecontemplated, e.g., less than 10, 9, 8, 7, 6, 5, 4 mm or at least 1-10mm or 2 mm up to about 25 mm distant; such targeting may be performed toavoid the macula itself, or not, as needed. Alternatively or example,such targeting may be used to place the material is a position to aninterior side of the eye where it does not intrude into the light paththrough the eye to the retina.

Drugs or other Therapeutic Agents for Delivery

The hydrogel may be used to deliver classes of drugs including steroids,Non-steroidal anti-inflammatory drugs (NSAIDS), intraocular pressurelowering drugs, antibiotics, or others. The hydrogel may be used todeliver drugs and therapeutic agents, e.g., an anti-inflammatory (e.g.,Diclofenac), a pain reliever (e.g., Bupivacaine), a Calcium channelblocker (e.g., Nifedipine), an Antibiotic (e.g., Ciprofloxacin), a Cellcycle inhibitor (e.g., Simvastatin), a protein (e.g., Insulin). The rateof release from the hydrogel will depend on the properties of the drugand the hydrogel, with factors including drug sizes, relativehydrophobicities, hydrogel density, hydrogel solids content, and thepresence of other drug delivery motifs, e.g., microparticles.

The hydrogel precursor may be used to deliver classes of drugs includingsteroids, NSAIDS (See Table 1), intraocular pressure lowering drugs,antibiotics, pain relievers, inhibitors or vascular endothelial growthfactor (VEGF), chemotherapeutics, anti-viral drugs etc. The drugsthemselves may be small molecules, proteins, RNA fragments, proteins,glycosaminoglycans, carbohydrates, nucleic acid, inorganic and organicbiologically active compounds where specific biologically active agentsinclude but are not limited to: enzymes, antibiotics, antineoplasticagents, local anesthetics, hormones, angiogenic agents, anti-angiogenicagents, growth factors, antibodies, neurotransmitters, psychoactivedrugs, anticancer drugs, chemotherapeutic drugs, drugs affectingreproductive organs, genes, and oligonucleotides, or otherconfigurations. The drugs that have low water solubility may beincorporated, e.g., as particulates or as a suspension. Higher watersolubility drugs may be loaded within microparticles or liposomes.Microparticles can be formed from, e.g., PLGA or fatty acids.

TABLE 1 NSAIDS that may be delivered. Item Drug Structure Solubility  1Ibuprofen

10 mg/ml @ pH 7  2 Meclofenamate Sodium

<50 μg/mL @ pH 7.2 50 mg/mL @ pH 9.0  3 Mefanamic Acid

40 μg/ml @ pH 7.1  4 Salsalate

 5 Sulindac

Practically insoluble below pH 4.5: Very soluble >pH 6  6 TolmetinSodium

Freely soluble in water  7 Ketoprofen

Not less than 0.25 mg/ml @ pH 7.35  8 Diflunisal

3.43 mg/ml @ pH 7  9 Piroxicam

0.03 mg/ml 10 Naproxen

Freely soluble at pH 8 11 Etodolac

Insoluble in water 12 Flurbiprofen

0.9 mg/mL 13 Fenoprofen Calcium

Slightly soluble in water 14 Indomethacin

@ pH 7 Form I: 0.54 mg/ml Form II: 0.80 mg/ml 15 Celecoxib

5 μg/ml 16 Ketorolac

10.5 mg/ml in IPB; 25 mg/ml as tromethamine salt. 17 Nepafenac

<1 mg/ml (The drug is available as 0.1% suspension)

In some embodiments, the therapeutic agent is mixed with the precursorsprior to making the aqueous solution or during the aseptic manufacturingof the functional polymer. This mixture then is mixed with the precursorto produce a crosslinked material in which the biologically activesubstance is entrapped. Functional polymers made from inert polymerslike PLURONIC, TETRONICS or TWEEN surfactants are preferred in releasingsmall molecule hydrophobic drugs.

In some embodiments, the therapeutic agent or agents are present in aseparate phase when crosslinker and crosslinkable polymers are reactedto produce a crosslinked polymer network or gel. This phase separationprevents participation of bioactive substance in the chemicalcrosslinking reaction such as reaction between NHS ester and aminegroup. The separate phase also helps to modulate the release kinetics ofactive agent from the crosslinked material or gel, where ‘separatephase’ could be oil (oil-in water emulsion), biodegradable vehicle, andthe like. Biodegradable vehicles in which the active agent may bepresent include: encapsulation vehicles, such as microparticles,microspheres, microbeads, micropellets, and the like, where the activeagent is encapsulated in a bioerodable or biodegradable polymers such aspolymers and copolymers of: poly(anhydride), poly(hydroxy acid)s,poly(lactone)s, poly(trimethylene carbonate), poly(glycolic acid),poly(lactic acid), poly(glycolic acid)-co-poly(glycolic acid),poly(orthocarbonate), poly(caprolactone), crosslinked biodegradablehydrogel networks like fibrin glue or fibrin sealant, caging andentrapping molecules, like cyclodextrin, molecular sieves and the like.Microspheres made from polymers and copolymers of poly (lactone) s andpoly (hydroxy acid) are particularly preferred as biodegradableencapsulation vehicles.

In using crosslinked materials which are described herein as drugdelivery vehicles, the active agent or encapsulated active agent may bepresent in solution or suspended form in crosslinker component orfunctional polymer solution component. The nucleophilic component,whether it be in the crosslinker or the functional polymer is thepreferred vehicle due to absence of reactive groups. The functionalpolymer along with bioactive agent, with or without encapsulatingvehicle, is administered to the host along with equivalent amount ofcrosslinker and aqueous buffers. The chemical reaction betweencrosslinker and the functional polymer solution readily takes place toform a crosslinked gel and acts as a depot for release of the activeagent to the host. Such methods of drug delivery find use in bothsystemic and local administration of an active agent.

A variety of drugs or other therapeutic agents may be delivered usingthese systems. A list of agents or families of drugs and examples ofindications for the agents are provided. The agents may also be used aspart of a method of treating the indicated condition or making acomposition for treating the indicated condition. For example, AZOPT (abrinzolamide opthalmic suspension) may be used for treatment of elevatedintraocular pressure in patients with ocular hypertension or open-angleglaucoma. BETADINE in a Povidone-iodine ophthalmic solution may be usedfor prepping of the periocular region and irrigation of the ocularsurface. BETOPTIC (betaxolol HCl) may be used to lower intraocularpressure, or for chronic open-angle glaucoma and/or ocular hypertension.CILOXAN (Ciprofloxacin HCl opthalmic solution) may be used to treatinfections caused by susceptible strains of microorganisms. NATACYN(Natamycin opthalmic suspension) may be used for treatment of fungalblepharitis, conjunctivitis, and keratitis. NEVANAC (Nepanfenacopthalmic suspension) may be used for treatment of pain and inflammationassociated with cataract surgery. TRAVATAN (Travoprost ophthalmicsolution) may be used for reduction of elevated intraocularpressure—open-angle glaucoma or ocular hypertension. FML FORTE(Fluorometholone ophthalmic suspension) may be used for treatment ofcorticosteroid-responsive inflammation of the palperbral and bulbarconjunctiva, cornea and anterior segment of the globe. LUMIGAN(Bimatoprost ophthalmic solution) may be used for reduction of elevatedintraocular pressure—open-angle glaucoma or ocular hypertension. PREDFORTE (Prednisolone acetate) may be used for treatment ofsteroid-responsive inflammation of the palpebral and bulbar conjunctiva,cornea and anterior segment of the globe. PROPINE (Dipivefrinhydrochloride) may be used for control of intraocular pressure inchronic open-angle glaucoma. RESTASIS (Cyclosporine ophthalmic emulsion)may be used to increases tear production in patients, e.g., those withocular inflammation associated with keratoconjunctivitis sicca. ALREX(Loteprednol etabonate ophthalmic suspension) may be used for temporaryrelief of seasonal allergic conjunctivitis. LOTEMAX (Loteprednoletabonate ophthalmic suspension) may be used for treatment ofsteroid-responsive inflammation of the palpebral and bulbar conjunctiva,cornea and anterior segment of the globe. MACUGEN (Pegaptanib sodiuminjection) may be used for Treatment of neovascular (wet) age-relatedmacular degeneration. OPTIVAR (Azelastine hydrochloride) may be used fortreatment of itching of the eye associated with allergic conjunctivitis.XALATAN (Latanoprost ophthalmic solution) may be used to reduce elevatedintraocular pressure in patients, e.g., with open-angle glaucoma orocular hypertension. BETIMOL (Timolol opthalmic solution) may be usedfor treatment of elevated intraocular pressure in patients with ocularhypertension or open-angle glaucoma.

In using the crosslinked composition for drug delivery as mentionedabove, the amount of crosslinkable polymer, crosslinker and the dosageagent introduced in the host will necessarily depend upon the particulardrug and the condition to be treated. Administration may be by anyconvenient means such as syringe, cannula, trocar, catheter and thelike.

Certain embodiments of the invention are accomplished by providingcompositions and methods to control the release of relatively lowmolecular weight therapeutic species using hydrogels. A therapeuticagent first is dispersed or dissolved within one or more relativelyhydrophobic rate modifying agents to form a mixture. The mixture may beformed into particles or microparticles, which are then entrapped withina bioabsorbable hydrogel matrix so as to release the water solubletherapeutic agents in a controlled fashion. Alternatively, themicroparticles may be formed in situ during cros slinking of thehydrogel.

In one method, hydrogel microspheres are formed from polymerizablemacromers or monomers by dispersion of a polymerizable phase in a secondimmiscible phase, wherein the polymerizable phase contains at least onecomponent required to initiate polymerization that leads to crosslinkingand the immiscible bulk phase contains another component required toinitiate crosslinking, along with a phase transfer agent. Pre-formedmicroparticles containing the water soluble therapeutic agent may bedispersed in the polymerizable phase, or formed in situ, to form anemulsion. Polymerization and crosslinking of the emulsion and theimmiscible phase is initiated in a controlled fashion after dispersal ofthe polymerizable phase into appropriately sized microspheres, thusentrapping the microparticles in the hydrogel microspheres.Visualization agents may be included, for instance, in the microspheres,microparticles, and/or microdroplets.

Embodiments of the invention include compositions and methods forforming composite hydrogel-based matrices and microspheres havingentrapped therapeutic compounds. In one embodiment, a bioactive agent isentrapped in microparticles having a hydrophobic nature (also termedhydrophobic microdomains), to retard leakage of the entrapped agent. Insome cases, the composite materials that have two phase dispersions,where both phases are absorbable, but are not miscible. For example, thecontinuous phase may be a hydrophilic network (such as a hydrogel, whichmay or may not be crosslinked) while the dispersed phase may behydrophobic (such as an oil, fat, fatty acid, wax, fluorocarbon, orother synthetic or natural water immiscible phase, generically referredto herein as an “oil” or “hydrophobic” phase).

The oil phase entraps the drug and provides a barrier to release by slowpartitioning of the drug into the hydrogel. The hydrogel phase in turnprotects the oil from digestion by enzymes, such as lipases, and fromdissolution by naturally occurring lipids and surfactants. The latterare expected to have only limited penetration into the hydrogel, forexample, due to hydrophobicity, molecular weight, conformation,diffusion resistance, etc. In the case of a hydrophobic drug which haslimited solubility in the hydrogel matrix, the particulate form of thedrug may also serve as the release rate modifying agent.

Hydrophobic microdomains, by themselves, may be degraded or quicklycleared when administered in vivo, making it difficult to achieveprolonged release directly using microdroplets or microparticlescontaining the entrapped agent in vivo. In accordance with the presentinvention, however, the hydrophobic microdomains are sequestered in agel matrix. The gel matrix protects the hydrophobic microdomains fromrapid clearance, but does not impair the ability of the microdroplets ormicroparticles to release their contents slowly. Visualization agentsmay be included, for instance, in the gel matrix or the microdomains.

In one embodiment, a microemulsion of a hydrophobic phase and an aqueoussolution of a water soluble molecular compound, such as a protein,peptide or other water soluble chemical is prepared. The emulsion is ofthe “water-in-oil” type (with oil as the continuous phase) as opposed toan “oil-in-water” system (where water is the continuous phase). Otheraspects of drug delivery are found in commonly assigned U.S. Pat. Nos.6,632,457; 6,379,373; and 6,514,534, each of which are herebyincorporated by reference. Moreover, drug delivery schemes as describedin commonly owned Compositions And Methods For Controlled Drug DeliveryFrom Biodegradable Hydrogels, now 60/899,898 filed Feb. 6, 2007, whichis hereby incorporated by reference herein, may also be used with thehydrogels herein.

Controlled rates of drug delivery also may be obtained with the systemdisclosed herein by degradable, covalent attachment of the bioactivemolecules to the crosslinked hydrogel network. The nature of thecovalent attachment can be controlled to enable control of the releaserate from hours to weeks or longer. By using a composite made fromlinkages with a range of hydrolysis times, a controlled release profilemay be extended for longer durations.

Biodegradation

The hydrogel is, in general, water-degradable, as measurable by thehydrogel being dissolvable in vitro in an excess of water by degradationof water-degradable groups. This test is predictive ofhydrolytically-driven dissolution in vivo, a process that is in contrastto cell or protease-driven degradation. The hydrogels can be selected tobe absorbable over days, weeks, or months, depending on the drugselected, disease being treated, the duration for release that isneeded, and the release profile of the specific drug selected. Someembodiments, however, are specifically directed to 30 to 120 days sincelonger periods of time allow for less user-control of the dosingregimen, a factor that may be important if the drug does not exert itsintended effect.

The biodegradable linkage may be water-degradable or enzymaticallydegradable. Illustrative water-degradable biodegradable linkages includepolymers, copolymers and oligomers of glycolide, dl-lactide, 1-lactide,dioxanone, esters, carbonates, and trimethylene carbonate. Illustrativeenzymatically biodegradable linkages include peptidic linkages cleavableby metalloproteinases and collagenases. Examples of biodegradablelinkages include polymers and copolymers of poly(hydroxy acid)s,poly(orthocarbonate)s, poly(anhydride)s, poly(lactone)s,poly(aminoacid)s, poly(carbonate)s, and poly(phosphonate)s.

Significantly, however, polyanhydrides or other conventionally-useddegradable materials that degrade to acidic components tend to causeinflammation in the eye. The hydrogels, however, may exclude suchmaterials, and may be free of polyanhydrides, anhydride bonds, orprecursors that degrade into acid or diacids. Instead, for example, SG(succinimidyl glutarate), SS (succinimidyl succinate), SC (succinimidylcarbonate), carboxymethyl hydroxybutyric acid (CM-HBA) may be used andhave esteric linkages that are hydrolytically labile.

If it is desired that the biocompatible crosslinked polymer bebiodegradable or absorbable, one or more precursors having biodegradablelinkages present in between the functional groups may be used. Thebiodegradable linkage optionally also may serve as the water solublecore of one or more of the precursors. For each approach, biodegradablelinkages may be chosen such that the resulting biodegradablebiocompatible crosslinked polymer will degrade or be absorbed in adesired period of time.

The crosslinked hydrogel degradation will generally proceed by thewater-driven hydrolysis of the biodegradable segment whenwater-degradable materials are used. If polyglycolate is used as thebiodegradable segment, for instance, the crosslinked polymer could bemade to degrade in about 1 to about 30 days depending on thecrosslinking density of the network. Similarly, a polycaprolactone basedcrosslinked network can be made to tend to degrade in about 1 to about 8months. The degradation time generally varies according to the type ofdegradable segment used, in the following order:polyglycolate<polylactate<polytrimethylene carbonate<polycaprolactone.Thus it is possible to construct a hydrogel with a desired degradationprofile, from a few days to many months, using a degradable segment.

Visualization Agents

A visualization agent may be used with the hydrogel; it reflects oremits light at a wavelength detectable to a human eye so that a userapplying the hydrogel can observe the gel.

Preferred biocompatible visualization agents are FD&C BLUE #1, FD&C BLUE#2, and methylene blue. These agents are preferably present in the finalelectrophilic-nucleophilic reactive precursor species mix at aconcentration of more than 0.05 mg/ml and preferably in a concentrationrange of at least 0.1 to about 12 mg/ml, and more preferably in therange of 0.1 to 4.0 mg/ml, although greater concentrations maypotentially be used, up to the limit of solubility of the visualizationagent. These concentration ranges can give a color to the hydrogelwithout interfering with crosslinking times (as measured by the time forthe reactive precursor species to gel).

Visualization agents may be selected from among any of the variousnon-toxic colored substances suitable for use in medical implantablemedical devices, such as FD&C BLUE dyes 3 and 6, eosin, methylene blue,indocyanine green, or colored dyes normally found in synthetic surgicalsutures. The visualization agent may be present with either reactiveprecursor species, e.g., a crosslinker or functional polymer solution.The preferred colored substance may or may not become chemically boundto the hydrogel. The visualization agent may generally be used in smallquantities, preferably less than 1% weight/volume, more preferably lessthat 0.01% weight/volume and most preferably less than 0.001%weight/volume concentration.

Additional machine-aided imaging agents may be used, such as fluorescentcompounds, x-ray contrast agents (e.g., iodinated compounds) for imagingunder x-ray imaging equipment, ultrasonic contrast agents, or MRIcontrast agents (e.g., Gadolinium containing compounds).

Viscosity

A composition with the precursors mixed therein can be made withviscosity suitable for introduction through a small gauge needle usingmanual force. A small gauge needle has a diameter less than the diameterof a needle with a gauge of 27, e.g., 28, 29, 30, 31, 32, or 33 gauge,with the gauge being specific for inner and/or outer diameters.Moreover, hollow-tube wires, as used in the intravascular arts, may beused to deliver the materials, including those with inn and/or outerdiameters equivalent to the small gauge needles, or smaller. Thus aviscosity of between about 1 to about 100,000 centipoise may be used;artisans will immediately appreciate that all the ranges and valueswithin the explicitly stated ranges are contemplated e.g., about 10 toabout 10,000 centipoise, less than about 5 to about 10,000 centipoise,less than about 100 or about 500 centipoise, or between about 1 andabout 100 centipoise. The viscosity may be controlled, e.g., by choosingappropriate precursors, adjusting solids concentrations, and reactionkinetics. In general, lower concentrations of precursors, increasedhydrophilicity, lower molecular weights favor a lower viscosity.

Viscosity enhancers may be used in conjunction with precursors. Ingeneral, the viscosity enhancers do not react with the precursors toform covalent bonds. While it is appreciated that precursors that aregenerally free of such bonding may sometimes participate in unwantedside reactions, these have little effect on the hydrogel so that theprecursors are “free” of such reactions. For instance, if the precursorsreact by electrophile-nucleophile reactions, the viscosity enhancers maybe free of electrophiles or nucleophiles that can form covalent bondswith functional groups of the precursors, even if there is some lowlevel of unwanted side reactions. Viscosity enhancers are, in general,hydrophilic polymers with a molecular weight of at least 20,000, or fromabout 10,000 to about 500,000 Daltons; artisans will immediatelyappreciate that all values and ranges between these explicitly statedvalues are described, e.g., at least about 100,000 or 200,000. Aconcentration of about 5% to about 25% w/w may be used, for instance.PEG (e.g., M.W. 100,000 to 250,000) is useful, for example. Viscosityenhancers may be free of electrophiles and/or nucleophiles. Viscosityenhancers may be fee of one or more functional groups such as hydroxyl,carboxyl, amine, or thiol. Viscosity enhancers may include one or morebiodegradable links as described herein for precursors. Viscosityenhancers can be useful to prevent precursors from running-off a tissuesite before the precursor's crosslink to form a gel.

Overview

Certain polymerizable hydrogels made using synthetic precursors areknown in the medical arts, e.g., as used in products such as FOCALSEAL(Genzyme, Inc.), COSEAL (Angiotech Pharmaceuticals), and DURASEAL(Confluent Surgical, Inc), as in, for example, U.S. Pat. Nos. 6,656,200;5,874,500; 5,543,441; 5,514,379; 5,410,016; 5,162,430; 5,324,775;5,752,974; and 5,550,187; each of which are hereby incorporated byreference to the extent they do not contradict what is explicitlydisclosed herein. None of these materials seem to be suited to useinside the eye or around the eye. One reason is that they polymerize tooquickly to be injected in a controlled fashion. Also, COSEAL andDURASEAL have a very high pH, which can be detrimental to ocular tissues(above pH 9). Another reason is that they apparently swell too much. Theswelling of COSEAL and DURASEAL has been measured using an in vitromodel in comparison to fibrin sealant (Campbell et al., Evaluation ofAbsorbable Surgical Sealants: In vitro Testing, 2005). Over a three daytest, COSEAL swelled an average of about 558% by weight, DURASEALincreased an average of about 98% by weight, and fibrin sealant swelledabout 3%. Assuming uniform expansion along all axes, the percentincrease in a single axis was calculated to be 87%, 26%, and 1% forCOSEAL, DURASEAL, and fibrin sealant respectively. FOCALSEAL is known toswell over 300%. And also needs an external light to be activated, so isnot well suited as an injectable drug delivery depot, especially in oraround the eye, which is sensitive to such radiation. Fibrin sealant isa proteinaceous glue that has adhesive, sealing, and mechanicalproperties that are inferior to COSEAL, DURASEAL, and other hydrogelsdisclosed herein. Further, it is typically derived from biologicalsources that are potentially contaminated, is cleared from the body bymechanisms distinct from water-degradation, and typically requiresrefrigeration while stored.

Some gel systems exist that relate to healing a wound or providing alens on the cornea, e.g., as in U.S. Pat. Nos. 5,874,500, 6,458,889,6,624,245 or PCT WO2006/031358 or WO2006/096586; other gels or systemsfor drug delivery are set forth in U.S. Pat. Nos. 6,777,000, 7,060,297,US2006/0182771, US2006/0258698, US2006/0100288, or US2006/0002963; eachof which are hereby incorporated by reference to the extent they do notcontradict what is explicitly disclosed herein.

Some systems to deliver drugs to the eye rely on topical eye drops. Forexample, after cataract and vitreoretinal surgery, antibiotics may needto be administered every few hours for several days. In addition, otherdrugs such as non-steroidal anti-inflammatory drugs (NSAIDS) may alsoneed to be given frequently. Often some of these eye drops, for exampleRESTASIS (Allergan) also has a stinging and burning sensation associatedwith its administration. RESTASIS is indicated for dry eye and has to beused by the patient several times a day. Similarly treatments for otherophthalmic diseases such as cystoid macular edema, diabetic macularedema (DME), and diabetic retinopathy also need administration ofsteroidal or NSAID drugs. Several vascular proliferative diseases suchas macular degeneration are treated using intravitreal injections ofVEGF inhibitors. These include drugs such as LUCENTIS and AVASTIN(Genentech) and MACUGEN (OSI). Such drugs may be delivered using thehydrogel systems herein, with the steps of repeated dosings beingavoided; e.g., not making new applications of the drug daily, weekly, ormonthly, or not using topical eye drops to administer the drug.

Several alternative drug delivery systems are known. These other systemsgenerally include intravitreal implant reservoir type systems,biodegradable depot systems, or implants that need to be removed(non-erodeable). The state of the art in this regard has been delineatedin texts such as “Intraocular Drug Delivery” (Jaffe et al., Taylor &Francis pub., 2006. However, most of these implants either need to beremoved at term, can detach from their target site, may cause visualdisturbances in the back of the eye or can be inflammatory themselvesbecause of the liberation of a substantial amount of acidic degradationproducts. These implants are thus made to be very small with a very highdrug concentration. Even though they are small, they still need to bedeployed with needles over 25G (25 gauge) in size, or a surgicalapproach delivery system for implantation or removal as needed. Ingeneral, these are localized injections of drug solutions into thevitreous humor or intravitreal implants that use abiodegradable-approach or a removable-reservoir approach.

For instance, localized injections delivered into the vitreous humorinclude anti-VEGF agents LUCENTIS or AVASTIN. POSURDEX (Allergan) is abiodegradable implant with indications for use being diabetic macularedema (DME) or retinal vein occlusions, with a 22 g delivery system usedfor delivery into the vitreous cavity; these are powerful drugs in ashort drug delivery duration setting. The therapeutic agent is indexamethasone with polylactic/polyglycolic polymer matrix. Phase IIItrials with POSURDEX for diabetic retinopathy are in progress.

And for instance, a Medidure implant (PSIVIDA) is used for DMEindications. This implant is about 3 mm in diameter, cylindrical inshape, and non-erodeable. It is placed with a 25 gauge injector deliverysystem, the therapeutic agent is fluocinolone acetonide, and has anominal delivery life of 18 months or 36 months (two versions). PhaseIII trials in progress.

Surmodics has a product that is an intravitreal, removable implant. Itis placed surgically, with a therapeutic agent being triamcinoloneacetonide. Its nominal delivery life is about two years. Its indicationis for DME. It is presently in about Phase I trials.

In contrast to these conventional systems, hydrogels can be made thatare biocompatible for the eye, which is an environment that isdistinctly different from other environments. The use of minimallyinflammatory materials avoids angiogenesis, which is harmful in the eyein many situations. Biocompatible ocular materials thus avoid unintendedangiogenesis; in some aspects, avoiding acidic degradation productsachieves this goal. Further, by using hydrogels and hydrophilicmaterials (components having a solubility in water of at least one gramper liter, e.g., polyethylene glycols/oxides), the influx ofinflammatory cells is also minimized; this process is in contrast toconventional use of non-hydrogel or rigid, reservoir-based ocularimplants. Moreover, certain proteins may be avoided to enhancebiocompatibility; collagen or fibrin glues, for instance, tend topromote inflammation or unwanted cellular reactions since these releasessignals as they are degraded that promote biological activity. Instead,synthetic materials are used, or peptidic sequences not normally foundin nature. Moreover, the hydrogels may be made without external energyand/or without photoactivation so as to avoid heating or degradation oftissues, bearing in mind that the eye is a sensitive tissue.Additionally, biodegradable materials may be used so as to avoid achronic foreign body reaction, e.g., as with thermally-formed gels thatdo not degrade. Further, soft materials or materials made in-situ toconform the shape of the surrounding tissues can minimize oculardistortion, and low-swelling materials may be used to eliminatevision-distortion caused by swelling. High pH materials may be avoided,both in the formation, introduction, or degradation phases.

Kits or Systems

Kits or systems for making hydrogels may be prepared. The kits aremanufactured using medically acceptable conditions and containprecursors that have sterility, purity and preparation that ispharmaceutically acceptable. The kit may contain an applicator asappropriate, as well as instructions. A therapeutic agent may beincluded pre-mixed or available for mixing. Solvents/solutions may beprovided in the kit or separately, or the components may be pre-mixedwith the solvent. The kit may include syringes and/or needles for mixingand/or delivery.

In some embodiments, the kit has at least one precursor and anapplicator. In some embodiments, a biodegradable, polymeric, synthetichydrogel is formed by the reaction of an 8 armed 15,000 MW polyethyleneglycol (PEG) having NHS-esters on each terminus of each arm withtrilysine (which has primary amine nucleophiles) in phosphate or otherbuffer solutions. Visualization agents (e.g., FD&C Blue #1) may beincorporated into the sealant material.

In some embodiments the kit's applicator includes (or consistsessentially of) syringes for syringe-to-syringe mixing. The deliverydevice is one of the syringes, and has a small bore tube with aLUER-lock on at least one end. After reconstitution of the product, anapplicator tube is attached to the delivery syringe and the hydrogel isapplied to the target tissue.

In some embodiments, kits having precursors and other materials asneeded to form a hydrogel in situ with a therapeutic agent may beprovided, with the component parts including those described herein. Insome aspects, features of the hydrogels can thus be chosen to makehydrogels that are minimally swelling, delivered through a small needle,can be put into an aqueous low viscosity preparation to gel afterplacement. The hydrogel is not inflammatory or angiogenic, relies onbiocompatible precursors, and is soft, hydrophilic, and conforming tothe space wherein it is placed. The hydrogel may be easily removable orself-removing, and can be biodegradable or suited to delivery to easilyaccessible areas without dispersal. It can be made so it is easy to mixand use, with an option to combine all the precursors in a singlecontainer. The hydrogel may be made with safe, all-synthetic materials.The hydrogel formulations may be made to be adhesive to tissues. Thedegradation and/or delivery rate may be controlled to fit the timeperiods described. Since the hydrogel is cross-linked, it will not comeout of the needle tract or other hole created for its delivery becauseit is shape-stable as deposited. The hydrogel depots have advantagesrelative to eye drops. Over 97% of topically administered eye drops arecleared via the tear ducts and do not end up penetrating the eye.Patient compliance may be enhanced by avoiding repeated dosing.

The use of fluent aqueous precursors to form a biodegradable drug depotallows for administration through small (e.g., 30 gauge) needles. Also,since the hydrogel can be made to not break down into acidic byproducts, the drug depots are well tolerated by sensitive tissues, suchas the eye. Due to this, the implants can be made rather large in size(e.g., 1 ml capacity) relative to implants that are made fromconventional biodegradable polymers, which are conventionally muchsmaller. Accordingly, some embodiments are hydrogels with volumesbetween about 0.5 to about 5 ml; artisans will immediately appreciatethat all the ranges and values within the explicitly stated ranges arecontemplated, e.g., 0.5 ml to about 1 ml. This makes such hydrogelseminently suited for periocular (episclereal or posterior subtenoninjections (PST)) drug depots.

While some of the agent in one of the hydrogels or other crosslinkedmaterials may be lost to the systemic circulation through a periocularroute, a significantly larger implant size has the capability to retaintherapeutic agent concentrations and accommodate larger implants toenable adequate transscleral diffusion of drugs across the sclera andinto the back of the eye, bearing in mind that the human sclera surfacearea is about 17 cm². The hydrogels also help in localizing the drug; byway of contrast, if a drug suspension or microparticles are injectedwithin the vitreous, they can migrate into the visual field andinterfere with vision.

Example 1 Drug Incorporation into Hydrogel

Two precursors and a diluent were prepared. The first precursor was an8-armed polyethylene glycol with a succinimidyl glutarate on theterminus of each arm, having a molecular weight of about 15,000. It wasprovided as a powder and blended with a dye (FD&A Blue) at aconcentration of 0.11% w/w. The second precursor was trilysine in a 0.2M sodium phosphate buffer at pH 8. A diluent for the first precursor wasprepared to be 0.01 M sodium phosphate, pH 4.8.

A drug (as indicated in Examples below) was mixed into drug intodiluent, and about 200 μl of the drug/diluent was drawn into a 1 mlsyringe. 66 mg of the first precursor powder was placed into a separate1 ml syringe. The two syringes were attached via a female-female luerconnector, and the solution was injected back-and-forth until the powderwas completely dissolved. The second precursor in its solution was drawn(200 μl) into a third syringe. With another female-female luerconnector, the first and second precursors were thoroughly mixed. Themixed solution was drawn into one of the syringes and attached to a 4inch length of silicone tubing that received the contents. Afterallowing a suitable reaction time, the tubing was cut into desiredlengths, and the gel inside pushed out with a mandrel. Resultinghydrogel plugs were, in general, 0.125 inch in diameter and about 6.4 mmthick.

Unless otherwise indicated, the analysis of drug release profiles wasascertained using high-pressure liquid chromatography (HPLC). The diskswere kept in a solution and the solution was periodically sampled andtested by HPLC to measure the concentration of drug in the solution.Total drug loading was determined by dissolving the disks in aqueoussolution or in the presence of an alcohol such as octanol at high pH andmeasuring the drug content in the disks. Drug loading was 5% (weight ofdrug/total weight of hydrogel including contents) unless otherwiseindicated.

Example 2 Release of Diclofenac Sodium

Diclofenac Sodium has a water solubility of about 1113 mg/L. It is ananti-inflammatory drug. It was loaded into a hydrogel as per Example 1and was released as indicated in FIG. 9. Essentially complete release ofthe drug was observed in about 8 hours.

Example 3 Release of Bupivacaine

Bupivacaine has a water solubility of about 86 mg/L. It is a painreliever that was converted from an HCl-salt to a free base to decreasewater solubility. It was loaded into a hydrogel as per Example 1 and wasreleased as indicated in FIG. 10. Sustained zero order release wasobserved over six days.

Example 4 Release of Nifedipine

Nifedipine has a water solubility of less than 1 mg/L. It is a calciumchannel blocker and Anti-hypertensive that relieves angina by increasingblood flow to the heart. It was loaded into a hydrogel as per Example 1and was released as indicated in FIG. 11. Sustained zero order releaseover 45 days.

Example 5 Release of Ciprofloxacin

Ciprofloxacin has a water solubility of 160 mg/L. It is an antibiotic.It was loaded into a hydrogel as per Example 1 and was released asindicated in FIG. 12, which shows testes at ph 9.0 (squares) or pH 7.4(circles). 50% of drug released by day three.

Example 6 Release of Mefenamic Acid

Mefenamic Acid is an NSAID for treating pain. It was loaded into ahydrogel as per Example 1 and was released as indicated in FIG. 13,which shows tests at ph 9.0 (squares) or pH 7.4 (circles). It wasreleased over about 15 days although further degradation to itscomponent parts at later times would release additional amounts of thedrug.

Example 7 Release of Indomethacin

Indomethacin is another NSAID for treating pain. It was loaded into ahydrogel as per Example 1 and was released as indicated in FIG. 14,which shows tests at ph 9.0 (squares) or pH 7.4 (circles). The Figureshows the release profile over about six days; further release wasobserved but not quantified.

Example 8 Release of Triamcinolone

Triamcinolone has very little solubility in water and is a syntheticcorticosteroid conventionally given orally, by injection, inhalation, oras a topical cream. It was loaded into a hydrogel as per Example 1except that the loading was about 4% instead of 5%, and was released asindicated in FIG. 15, which shows tests up to about a week.

Example 9 Release of Dexamethasone

Dexamethasone is a glucocorticoid-type steroid hormone. It acts as ananti-inflammatory and immunosuppressant. It was loaded into a hydrogelas per Example 1 and was released as indicated in FIG. 16. The Figureshows the release profile over about six days; further release wasobserved but not quantified.

Many embodiments have been set forth herein. In general, components ofthe embodiments may be mixed-and-matched with each other as guided forthe need to make functional embodiments.

1. A method of treating an ophthalmic disease affecting an eye of apatient comprising forming a covalently-crosslinked hydrogel in situ ata site in an eye, wherein the hydrogel comprises a therapeutic agentthat is released into the eye to treat the ophthalmic disease.
 2. Themethod of claim 1 wherein the disease is a back-of-the eye disease. 3.The method of claim 2 wherein the back-of-the-eye disease is a selectedfrom the group consisting of wet macular degeneration, dry maculardegeneration, diabetic macular edema, cystoid macular edema, anddiabetic retinopathy.
 4. The method of claim 2 wherein theback-of-the-eye disease is an ocular disease of a posterior segment ofthe eye that affects a retina, macula or choroid, with said diseaseleading to a visual acuity disturbance, loss of sight, or blindness. 5.The method of claim 1 wherein the therapeutic agent is released over aperiod of time that is at least about three days.
 6. The method of claim1 wherein a time at which a cumulative 80% w/w of the therapeutic agenthas been released is between about 14 and 120 days.
 7. The method ofclaim 1 wherein the site is in a sclera of the eye.
 8. The method ofclaim 1 wherein the site is substantially disposed between a sclera anda conjunctiva.
 9. The method of claim 1 wherein the site is a potentialspace of the eye.
 10. The method of claim 9 further comprisingpuncturing a conjunctiva to access the potential space.
 11. The methodof claim 9 comprising mechanically creating the potential space.
 12. Themethod of claim 9 wherein the potential space is natural.
 13. The methodof claim 1 wherein the site is a vitreous of the eye or a posteriorchamber of the eye.
 14. The method of claim 1 wherein the hydrogel, whenformed, has a volume of between about 0.25 ml and about 1.5 ml.
 15. Themethod of claim 1 wherein the hydrogel, when formed, has a volume ofless than 0.5 ml.
 16. The method of claim 1 wherein the hydrogel islow-swelling, as measurable by the hydrogel having a weight increasingno more than about 50% upon exposure to a physiological solution fortwenty-four hours relative to a weight of the hydrogel at the time offormation.
 17. The method of claim 1 wherein the hydrogel iswater-degradable, as measurable by the hydrogel being dissolvable invitro in an excess of water by degradation of water-degradable groups.18. The hydrogel of claim 1 wherein the water-degradable groups areesters.
 19. The method of claim 1 wherein the hydrogel is formed bycombining a first synthetic precursor comprising nucleophilic groupswith a second synthetic precursor comprising electrophilic groups toform covalent crosslinks by reaction of the nucleophilic groups with theelectrophilic groups to form the biocompatible hydrogel.
 20. The methodof claim 19 further comprising injecting an aqueous mixture of theprecursors to the site.
 21. The hydrogel of claim 20 wherein thepolymeric hydrophilic portions comprise poly(ethylene) glycol repeats.22. The method of claim 1 wherein the hydrogel is formed by combining afirst synthetic precursor with a second synthetic precursor.
 23. Themethod of claim 1 further comprising a particle entrapped within thehydrogel, with the phase comprising the therapeutic agent.
 24. Thehydrogel of claim 23 wherein the particle is selected from the groupconsisting of a liposome, a micelle, and a hydrophobic particle.
 25. Themethod of claim 1 comprising the therapeutic agent as a suspension in anaqueous phase of the hydrogel.
 26. The hydrogel of claim 1 wherein thetherapeutic agent is selected from the group consisting ofdexamethasone, nifedipine, a steroid, an inhibitor of vascularendothelial growth factor, a small molecule drug, a protein, a nucleicacid, and a growth factor.